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Comprehensive Income (Loss) - Additional Information (Detail) $ in Millions | 3 Months Ended
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Dec. 31, 2020 USD ($)
Equity [Abstract] |
Changes in accumulated other comprehensive loss, net of related taxes | $ 1

X
- References No definition available. + Details
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Namespace Prefix: | us-gaap_
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Period Type: | duration

X
- Definition Changes in accumulated other comprehensive income loss net of related tax. + References No definition available. + Details
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Namespace Prefix: | wmg_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
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